Posted
by
Soulskillon Saturday April 26, 2014 @01:46PM
from the interstellar-stalker-hiding-in-the-bushes dept.

An anonymous reader writes "Astronomer Kevin Luhman just found the 7th closest star to the sun. It's a mere 7.2 light-years away, discovered using NASA's Spitzer and WISE telescopes. How could it exist so close for so long without us knowing? It's a brown dwarf — barely a star at all. 'Brown dwarfs are star-like objects that are more massive than planets, but not quite massive enough to ignite sustained fusion in their cores. Hydrogen fusion is what powers the Sun, and makes it hot; it's the mighty pressure of the Sun's core that makes that happen. Brown dwarfs don't have the oomph needed to keep that going.' This small almost-star is downright chilly at around 225-260 Kelvin. That's -48 to -13 C (or -54 to 9 F). As Phil Plait points out, that's not much different from the temperature in the freezer in your kitchen. He adds, 'It implies this object is very old, too, because it would've been a few thousands degrees when it formed, and would take at least a billion years to cool down to its current chilly temperature. It's hard to determine how old it actually is, but it's most likely 1-10 billion years old. It has a very low mass, too, probably between 3 and 10 times the mass of Jupiter. That's pretty lightweight even for a brown dwarf. And here's another amazing thing about it: It might be a planet. What I mean is, it may have formed around a star like a planet does, then got ejected by gravitational interactions with other planets.'"

You try spotting something that cold and not much bigger than jupiter 7 light years away! I'm incredibly impressed they've managed to spot it at all and should be congratulated since it'll barely even register in the infrared never mind visible light.

I keep hearing about "Dark Matter" as an explanation for how galaxies don't fly apart due to the force generated by their rotation, but I can't help thinking that all that mass we're looking for in galaxies could be stuff like this. Regular matter that just doesn't generate enough heat or light for us to have noticed prior to this.

Could the question of how galaxies rotate be answered by large quantities of objects such as these?

That's part of the MACHO hypothesis regarding dark matter. We could explain away dark matter with trillions of brown dwarfs but that doesn't seem satisfactory for astronomers and cosmologists. For some reason (big bang and cosmic background calculations etc.) we know think that baryonic (regular matter) is only about 4% of the universe's amount of mass-energy and about 25% of non-baryonic dark matter is needed to make it all fit. Not enough baryonic matter to have enough brown dwarfs playing the role of dark matter in/around galaxies.

Actually it's galactic rotation curve stuff: you can show what the observed vs. dark mass difference is by looking at the motion of stars along the plane of the galaxy. And when you start to propose that it's all asteroids and brown dwarfs, you run into problems - because if there were so many out there, then why don't they ever get heated up by all the radiation they'd be absorbing? And why don't they seem to ever meaningfully collide and experience other types of interactions (the famous bullet nebula pic

It is not just the comological level, but searches have been done for small objects roaming around the galaxy by looking for micro lensing events and occlusion events where rogue planets or objects move in front of other stars. If a large portion of the missing mass needed for the galaxy rotation curve were these planets, you can work out the chances of such objects passing in front of the stars being observed for such effects, and find that we should have seen way more than was actually observed.

I really can't stand the Dark Matter & Dark Energy theories; it's just the luminescent ether theory in a new guise.

I strikes me that it's far more likely that our measurements are terrible or we have a basic misunderstanding, rather than inventing a whole new class of matter that has to make up 96% of the universe to make the figures balance.

Then again I was actually disappointed when the LHC announced a 7-sigma result for the Higgs Boson...

I strikes me that it's far more likely that our measurements are terrible or we have a basic misunderstanding, rather than inventing a whole new class of matter that has to make up 96% of the universe to make the figures balance.

And yet even after we have repeatedly asked you to show your math leading to your hypothisis, you once again refuse to do so!

Current theory that you say is wrong is the exact same thing that gave us computers, the very tool you are using to state the theory is wrong.What has *your* theory given technology lately? One thing? two? Once you catch up to the hundreds of scientific fields that have brought us billions of tangable products - and also explains the missing mass better - we will continue to call yo

I totally agree with you. I mean - here's the thing that's always bothered me - if there is SO MUCH F-ing dark matter and dark energy then how is it so mysteriously EVERYWHERE ELSE in the universe but not anywhere near here? If the universe has been permeated by so much of this stuff there's no reason to believe it doesn not permeate our local little section of that universe is there?

This is why I'm with you: "dark matter" and "dark energy" are really just placeholders signifiying our model of astrophysi

It may permeate us. We just don't know.If dark matter is really not interacting with anything except that it causes gravity, how would we know? The stuff could be spread out so much between the stars that it is at a not-measurable density.Normal matter tends to clump together due to gravity. What if dark matter doesn't do that? We just don't know.

Having said that: I don't like dark matter and dark energy either. I just don't have enough data to dispute it.

Let's see, this brown dwarf is unusually small, and still between 3-10x the mas of Jupiter. Jupiter is about 5% the mass of the sun, meaning this dwarf is 15%-50%solar masses. Meanwhile even the very largest stars such as VY Canis, which is larger than the orbit of Jupiter, is actually estimated at only 17 solar masses, and the vast majority of stars are actually various dwarfs not so unlike our own. So, assume 10 dark sub-dwarf "stars" for every visible star and you've just doubled the mass of the gala

Now do that 20 more times and come back with an explanation as to why all that matter doesn't ever seem to interact. You're proposing to solve dark matter by saying there's about 200 brown dwarfs per star. How come they don't collide? Why didn't they collapse into just being, you know, stars?

We know why we'd have trouble finding near cold objects: the sky is relatively poorly lit, and so you have to hope to see them crossing or occluding another light source.

Well, assuming they didn't collide they also couldn't very well collapse into true stars, they just don't have enough mass. And assuming they're basically gaseous (mostly hydrogen after all) even a near-direct collision wouldn't necessarily cause a significant increase in mass of the larger surviving "fragment".

As for where they are, how about the outside rim of the galaxy? It would seem to me that the further you get from the heart of a young galaxy the thinner the gas clouds get spread, the less materia

Then how do they get there? For that matter, how do they stay there? Any gravitational interaction strong enough to toss them out of the galactic disk should be easily observable, and any orbital path around the center of the galactic mass should bring them back into the disk fairly frequently.

Why do you assume they didn't form there? At one point the entire galaxy was one big gaseous disc. Smaller eddies then formed within he disc to form proto-stellar discs that eventually became stars, just as eddies within those stellar discs eventually became planets. Stellar discs that formed in the thinner outer reaches of the galactic disc would presumably contain less mass and end up forming smaller bodies that were still in a basically circular orbit around the galactic hub. They'd never get apprecia

Again: you're proposing that somehow, 96% of the mass of the universe is in unseen brown dwarfs that are all floating around the edge of the galactic disk.

That is a huge amount of mass, to the point that it would be more significant then all the other mass in the galaxy. If this mass is not evenly distributed, then it would both form a binary system with the galaxy, and also promptly start collapsing itself into actual stars and a much denser body.

Okay, I'm not actually specifically arguing against the existence of Dark Matter, simply pointing out that one of the major anomalies that led us to initially speculate that it existed - anomalous galactic revolution - has been largely explained with modern conventional physics. Supplement GR with a relatively small number of nonluminous halo objects and you can completely explain galactic rotation without increasing galactic mass 20-fold. And there's no particular reason to assume that collisions between

Actually, no. If the majority of mass is within the radius of the outside stars then they would be rotating more slowly than the inner stars. If instead you have the bulk of the mass of the galaxy distributed outside the visible galactic rim then you have a situation where the visible "spokes" of the "bicycle wheel" will more closely match speed with the invisible "tire", regardless of their distance from the hub. Which is exactly the situation we're seeing.

But how do you explain why we don't detect these hundreds of objects in front of other stars?

You're assuming these transits would occur frequently and that we actually have the equipment pointed at the sky to detect them. Even if there were 200 times as many brown dwarfs as stars in the galaxy, actually seeing one pass in front of another star would be an extremely rare occurrence and we'd only detect if we were looking right at that star. Even then we'd only detect a small decrease in light and we'd be unable to distinguish it from the transit of a planet with a long orbital period. Also, cons

You're assuming these transits would occur frequently and that we actually have the equipment pointed at the sky to detect them.

Which parts of the MACHO theory and experiments didn't you understand? The ones that said "it's the late 1980s, and we've been running these observational programmes for several years and we're not seeing enough interactions to explain the gravitating mass that we know needs to be there"? Or the ones that said "it's the mid-1990s, and we're still not seeing enough interactions, but

How come they don't collide? Why didn't they collapse into just being, you know, stars?

Even at 200 times, collisions would be extremely rare. And the collision would be a non-event as far as the earth is concerned. Why don't they collapse into stars [assuming the collision produced a star with sufficient mass to be a star]. Maybe they are? Still the collisions would be so rare that we'd almost certainly never witness the event.

Here's the problem: you can't argue collisions would be rare. Collisions in the accretion disk of a gravitational body are extremely rare, but an object like a black hole is very bright because over the life time of the universe that's still a lot of collisions relatively.

The issue is, you're adding 200 times the number of entities and really underestimating that value, that's 200 brown dawrfs, larger then Jupiter, within the local neighborhood of Sol alone, along with another 400-600 around Alpha Centauri,

We know there are a lot of red dwarfs in the vicinity of Sol, but we don't know that this trend continues throughout the galaxy because they're hard to observe.

Of course, that's % of stars we can see. The problem is, the math says of that % we can see, they only make up about 4% of all matter in the universe.

Which again, gets to the problems of scale. 20 times more stuff that we somehow never see is a lot. And it's not just that we never see it - it's that somehow it avoids clumping up into being matter we

There almost certainly are more brown dwarves than other star type, but their relative mass is tiny. About 1% of a solar mass. So to account for dark matter, you'd need over 1000 brown dwarves for each and every other star in the galaxy.

Well maybe, but if this thing was never fusing was it ever really a star? And if it was fusing, but has now completely stopped, then the question is did it stop being a star while still orbiting it's primary, and thus become a planet first, or did it get ejected as a star and become a planet later? For that matter is there really such a thing as a rogue planet? Planet means wandering star, and we now know that it's only the act of orbitting a star that causes a planet to "wander" across the stellar backg

Sorry for the double-post, didn't realize I wasn't logged in when I posted this previously

I keep hearing about "Dark Matter" as an explanation for how galaxies don't fly apart due to the force generated by their rotation, but I can't help thinking that all that mass we're looking for in galaxies could be stuff like this. Regular matter that just doesn't generate enough heat or light for us to have noticed prior to this.

Could the question of how galaxies rotate be answered by large quantities of objects such as these?

The Wikipedia article on dark matter [wikipedia.org] discusses this in depth. Although I'm no astrophysicist and can't vouch for the article's accuracy, it does outline some of the reasons why those studying it believe that objects like this cannot account for the amount of dark matter required to explain how galaxies behave.

Your question is whether Dark Matter could be real and observed MACHOs [wikipedia.org].
The other main option is that Dark Matter could be hypothetical WIMPs [wikipedia.org]
Numerous experiments have ruled out MACHOS as making up the bulk of Dark Matter. The missing mass problem is not solved by MACHOs.
At the moment the WIMPS are beating the MACHOS.
See also History of the search for Dark Matter [wikipedia.org]

These object are composed of ordinary every day matter so they interact with electromagnetic radiation. For instance, this particular object was detected by infrared radiation.

Observation of the rest of the universe shows more gravitational interaction than electromagnetic interaction versus what you would expect from ordinary matter. "Dark Matter" and "Dark Energy" are proposed particle types that do not interact electromagnetically but to interact with other forces. Other proposals model the forces differ

Kudos for writing 225-260 Kelvin and not 'degree Kelvin' or 'Kelvins' in the summary. Slate f'ed up though. They wrote 'Kelvins'. I have seen even reputable scientific writings using degrees prefix with Kelvin. It's very disheartening to see that even some scientists don't get it that you don't use degrees when talking about absolute temperature.

Kudos for writing 225-260 Kelvin and not 'degree Kelvin' or 'Kelvins' in the summary. Slate f'ed up though. They wrote 'Kelvins'.

Umm, sorry, but you're wrong. As an SI unit, a "kelvin" (yes, with a lowercase k) is pluralized using the same grammatical rules as others (e.g., volts, ohms, etc.). Its abbreviation is an uppercase K.

So, "225-260 kelvins" or "225-260 K" is correct, according to official SI standard.

If you want to be pedantic, be sure you have a clue concerning what you're talking about.

(And regardless, I think this is a rather stupid thing to get too pedantic about. The previous standard, before 1968, referred to it as "degrees Kelvin" just like all the other temperature standards. I understand that the SI conventions are trying to maintain consistency across all units, but it's weird when that also results in breaking consistency with all other units that deal with the same type of measurement. I'm not saying it's wrong, and official scientific documents shoudl get it right, but in normal language... I think this is a rather silly think to get worried about, since it actually breaks other linguistic conventions of standard language.)

And by the way, before somebody starts objecting to my comment about common language usage by saying that "kelvins" and not "degrees Kelvin" represents an absolute scale or something, rather than a "degree" -- that's a bogus argument. Anyone who works with "degrees Rankine" knows that (1) it's always Rankine, not rankine, (2) it's never pluralized as "rankines" as "kelvins" is, (3) the abbreviation should contain the degree symbol, and (4) the only people who say "Rankine" instead of "degrees Rankine" are

I doubt it because we would be deluged with holidaying spherians every long weekend. Earth beaches are the best. Also the construction process would have generated a lot of debris. Seriously, it is too close not to be noticed as such. If they were humans there would be trillions of them in there. Even if it was a ringworld sort of thing with a collapsed civilisation, there would be ships coming past and making radio noise, exhaust, etc.

I doubt it because we would be deluged with holidaying spherians every long weekend. Earth beaches are the best. Also the construction process would have generated a lot of debris. Seriously, it is too close not to be noticed as such. If they were humans there would be trillions of them in there. Even if it was a ringworld sort of thing with a collapsed civilisation, there would be ships coming past and making radio noise, exhaust, etc.

Why do you think you have any idea what we would see or not see?

Imagine you were living with circa 1800 AD technology, and were looking for evidence of another civilization with circa 2014 technology. Keep in mind that this 200 year difference is nothing compared to the difference between modern technology and the technology of a race capable of building a Dyson sphere.

Perhaps you would use a rudimentary telescope to look out to sea. You would rule out any ships, since the weird objects you see don't have

Imagine you were living with circa 1800 AD technology, and were looking for evidence of another civilization with circa 2014 technology. Keep in mind that this 200 year difference is nothing compared to the difference between modern technology and the technology of a race capable of building a Dyson sphere.

The existence of the advanced civilisation would be obvious to us because they'd be in our villages raping our women. So maybe aliens wouldn't be doing precisely that, but if they are anything like us they would be curious and hungry for resources.I think the it is significant that the only debris found on the lunar surface was put there by humans. Any sort of exploration of our solar system would have left debris, garbage, broken vehicles, etc. And if somebody invested in a Dyson sphere only 7 light years

It might not be a Sphere itself, but my mind went there as well. If you have something 'refrigerator warm' in the middle of space, you can extract useful energy from it, and especially when the damn thing isn't on fire, materials. I'm thinking of some sort of sphere with millions of space elevators dangling down from the inside to the planet's surface, or something of that nature.

[insert hundreds of pages of math]

Perhaps a decent place for humans to do "My First Space Sphere" without all the stresses invo

A Dyson sphere might be radiating at 2.725 K, the microwave background temperature of the Universe, as the beings in it might have found a way to violate the 2nd law, via such things as a molecular ratchet, or brownian ratchet, and the Universe might be full of 2.725 K radiating things. The best way to hide a Dyson sphere is to make it the same temperature as the surroundings, and if it's not the same temperature, you may assume it's not a Dyson sphere.

Also life even on this planet does not require a star, or light and photosynthesis, just a sufficiently high head, or "waterfall" of caloric, i.e. a large temperature gradient. See the Wikipedia page on Hydrothermal vent, http://en.wikipedia.org/wiki/H... [wikipedia.org].

It can't be a Dyson sphere because it is not big enough to encompass a star.It could theoretically be an artificially made object of similar properties. However, that is IMHO less likely than an ancient brown dwarf or a rogue planet.

it may have formed around a star like a planet does, then got ejected by gravitational interactions with other planets.

But if Jupiter interacts with anything, Jupiter isn't going to get ejected. The remaining object must have been a sizeable star.This star must be warm deeper down. I wonder if it is a good place for life.

The Sun is ~1 AU away, the three Alpha Centauri stars are 4.24 to 4.37 l.y. away, Bernard's star is just under 6 l.y. away, and the two Luhman 16 brown dwarfs are just over 6.5 l.y. away. The position of Earth in its orbit is not enough to make any of those exceed 7.2 light years. this is either the 8th closest star that we know of, or it is not considered a star at all if you don't want to count brown dwarfs (or might be pushing the lower limit of what is a brown dwarf).

I don't think brown dwarf stars are really going to be much of a problem. They're hard to spot when they're 7 light years away, but they're still really big objects that are highly likely to appear to be moving through space from the perspective of any interstellar craft. Any such craft can be expected to have telescopes and something like this is virtually certain to show up through the telescope occluding other objects when it's closer. At the kinds of distances where it would be obvious there's still ple

The Wikipedia article on rogue planets discusses ways in which they could retain an atmosphere, warmth, and liquid water. If we knew one of these was in the neighborhood, and knew it was going somewhere interesting, we could use it as a ship. It's possible that we could get to one in a few centuries of travel, and then perhaps colonize it, and ride it the rest of the way to our ultimate destination. That's assuming wherever the rogue planet was going was more interesting and/or less deadly than wherever

If this were an object that coalesced away from any (other) protostellar discs, it may conceivably have small objects orbiting it. Since there wouldnt have been a "fusion event" to blow away the remaining gas and dust of the original cloud it formed from, any objects that coalesced near to the central sub-brown dwarf would not have been pushed out by the radiation pressure.

This means that gravitationally bound satellites close enough to be quite warm indeed just from tidal heating could be possible with "ob

The idea was that if it is metal rich, then the chances of rocky bodies that are much smaller/less dense than it can be tidally heated, and with that tidal heating, be able to support life. (say, chemotrophic microbes.)

Spectroscopic analysis of the object will only reveal its atmospheric composition. Lensing analysis (from a transit) would better refine mass estimates, which could help refine the internal composition, but much like our own gas gi

Well, it's only 7.2 lightyears away, so you don't need an FTL drive, you just need a LOT of patience. But what you really need is some way to cheaply get the mass away from a star's gravitational field. True, it's quite a small star, but at 3-10 times Jupiter's mass, it will take 9-90 times as much energy to extract it. (That's an estimate, not a calculated answer...but escape velocity goes up faster than the mass, or you'd almost never get a black hole.)

Obviously, but what worries me is that Relativity is correct that any form of FTL travel can inherently be repurposed as a time machine to travel into your own past. The integrity of lottery will be destroyed forever, and the complete collapse of civilization can't be far behind.

Not any form of FTL travel. Warp drives as currently proposed don't allow travelling into the past andthere might be tweaks to relativity or other as yet unknown methods like worm holes, etc.. that allowfaster travel.

AC is correct, both of those forms do still allow at the very least communication with the past if employed in a larger construct. Basically in the simplest form it relies on the fact that at relativistic speeds the Lorentz transformation rotates the space-time axes such that if some sublight traveler is moving at relativistic speeds relative to Earth, then certain directions that they perceive as space will be perceived by us as time. An FTL traveler departing from that relativistic frame can then travel

Actually estimates are that the red giant transition is 4 to 7 billion years out, so the Andromeda collision will roughly coincide with the lower end of estimates of our sun's lifespan in it's current state. It could also turn out that it will have another 3 billion years after the the collision begins.

True, but that's a separate issue from our sun exploding into a red giant. And really, both problems have the same relatively simple solution - move the Earth. It should be possible to start the process even with technology currently being developed - fusion-powered ion drives on the moon could slowly tug the Earth further from the sun. Sure it'd be incredibly slow, but we've got billions of years to get the job done. If we eventually master mass-energy conversion (a domesticated black hole should do the

If it is big enough to ignite fusion, then it is a star. A mass of about J8 (eight Jupiters) is needed to fuse deuterium. Most likely, that is not happening, or it would not be so cold. So it is not a star. But I don't think it is a planet either, because it is only a planet if it is orbiting a star. So I don't know what it is called.

I think I read somewhere that the inner core temperature of Jupiter is higher than it should be, and chemical engineering 101 says if heat out minus heat in not equal zero, then there is heat generated. The inner lava temperature of Earth is sustained mostly by K40 and U235 decay, besides minor asteroid impacts. So the inner temperature of Jupiter is also sustained probably by the same thing, and not fusion, as it is hard to imagine Jupiter without an iron-nickel core, and lava, and then a hydrogen atmosphe

Ditto for this "nonstar," it's hot for the same reasons that the inside of the Earth and Jupiter is hot, mostly K40 and U235.

Actually, probably not. There wasn't much potassium and uranium at the orbital position where proto-Jupiter formes, compared to water ice. So most models of the formation of Jupiter (and the rest of the Solar system) have a proto-Jupiter forming largely of water-ice, then going into runaway growth at about that mass and building up huge additional amounts of hydrogen and helium from t